cpufreq: remove unnecessary cpufreq_cpu_{get|put}() calls

struct cpufreq_policy is already passed as argument to some routines
like: __cpufreq_driver_getavg() and so we don't really need to do
cpufreq_cpu_get() before and cpufreq_cpu_put() in them to get a
policy structure.

Remove them.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>